1. Field Of The Invention
This invention relates to a windshield wiper motor used for driving a wiper linkage to wipe rain drops and the like on a windshield surface.
2. Description Of The Prior Art
Heretofore, there has been used a windshield wiper motor incorporated with, for example, an auto-stopping mechanism as shown in FIG. 8.
A windshield wiper motor 101 shown in FIG. 8 is equipped with an armature 102 and reduction gear 103 for reducing rotational speed of said armature 102, and equipped with an auto-stopping switch 105 for stopping a wiper blade A shown in FIG. 7 at a stopping position securely to a worm wheel that is the final gear of said reduction gear 103.
Said auto-stopping switch 105 is disposed with a circular first contact plate 110 cut off in fan-like shape at a part thereof and a second contact plate 111 positioned in the cutout portion of said first contact plate 110, separated from said first contact plate 110 and jutting out from the outer periphery of said first contact plate 110 on one side of said worm wheel, and is equipped with a first contact 113 connected to a power source 112 and an armature 102 and possible to contact only with said second contact plate 111 and a second contact 115 connected to an OFF-terminal 114a of a wiper switch 114 and possible to contact with both said first and second contact plates 110 and 111. And said first contact plate 110 is grounded, a high-speed terminal of the windshield wiper motor 101 is connected to a high-speed terminal 114c of the wiper switch 114 and a low-speed terminal of the windshield wiper motor 101 is connected to a low-speed terminal 114d of the wiper switch 114.
Moving a movable contact 114b of said wiper switch 114 to the OFF-terminal 114a from the high-speed terminal 114c or the low-speed terminal 114d, the wiper blade A is driven in the vicinity of the stopping position by continuing the power supply to the armature 102 because the second contact 115 of the auto-stopping switch 105 is in contact with the first contact plate 110 and grounded when the wiper blade A is not sited at the stopping position shown with a solid line in FIG. 7. And the power supply to the motor is cut off when the second contact 115 separetes from the first contact plate 110, however the wiper blade A is further moved by the inertial force. When said wiper blade A reaches in the stopping position, the first and second contacts 113 and 115 are in contact with the second contact plate 111 of the auto-stopping switch 105 and the wiper blade A is stopped immediately at the stopping position by braking the armature 102 dynamically.
However, in the aforementioned conventional windshield wiper motor 101, when the wiper switch 114 is changed into OFF-operation in order to stop the wiper blade A at the stopping position in a state in which snow stands in the vicinity of the stopping position by wiping snow with the wiper blade A in snowfall, the wiper blade A hits against the snow gathered in the vicinity of said stopping position of the wiper blade A and returns in the opposite direction as a reaction from the gathered snow. The position in which the wiper blade A hits against the gathered snow corresponds to a position in which the second contact 115 of the auto-stopping switch 105 is switched over from the contact with the first contact plate 110 to the contact with the second contact plate 111, said second contact 115 is in contact with a space between the first and second contact plates 110 and 111 and the armature 102 is in a state the power supply is cut off. Accordingly, the second contact 115 touches again the first contact plate 110 by the reaction from the gathered snow and the armature 102 is supplied with electric power, and a phenomenon that the wiper blade A hits repeatedly against the snow by the rotation of said armature 102 and the reaction from the snow, that is, chattering occures. Thereby the second contact 115 of the auto-stopping switch 105 sparks every time it touches the first contact plate 110 and the resinous worm wheel is deformed partially owing to the heat caused by sparking, there is a problem since the working of the windshield wiper motor 101 may be hindered by the deformation of the worm wheel.